1. Field of the Invention
The present invention pertains to antennas having a rotating support on which there is mounted at least one vertical array of radiating dipoles and at least one vertical reflector formed by wires.
2. Description of the Prior Art
Antennas such as these are known and are used in the field of HF waves. In the case of two arrays of dipoles, these antennas most usually have only one feeder line which generally goes through the support and feeds either of the two arrays by means of a switch-over unit.
The azimuthal angle of aim of prior art antennas can be easily adjusted in any direction by rotating the support. The angle of aim in elevation and the configuration of the antenna can be adjusted by means of switch-over devices enabling the connection, as desired, of all or a part of the dipoles of one and the same array of dipoles.
In these known antennas, the arrays of dipoles are formed by full wave conductive wire dipoles formed by conductive wires held between supporting beams by arrangements of cables, insulators, counterweights, pulleys etc. Thus, the dipoles are arranged in a sort of stretched curtain, in a vertical plane, between the supporting beams.
This curtain, which comprises the dipoles of an array, has a space factor that is greater than the overall dimensions of all the dipoles of the array. Under the effect of the wind, the curtain gets deformed causing, in particular, variations in input impedance of the antenna and mechanical problems. The result thereof is that the known rotating antennas are unusable at wind speeds starting from levels that are always far smaller than the maximum speed for which the stability of the antenna is ensured. This curtain which is used for the positioning of the dipoles also has other drawbacks: it is subjected to heavy stresses from the loads formed by deposits of ice. It makes it difficult to carry out the operations of hoisting or lowering the rotational antenna as well as servicing operations in the curtain.
As for the reflective curtain or curtains of known rotating antennas, they are generally constituted by a single sheet formed by horizontal wires and catenaries, and this sheet is held only by the top and by the bottom. Here too, climatic conditions give rise to deformations which can harm the working of the antenna.